The invention relates to a detector for detecting information carried by signal having a sawtooth-like shape, and more particularly to a detector having a filter and a comparator to detect the information carried by a signal having a sawtooth-like shape.
Along with advances in optical disc technologies, a new generation of the optical disc rewritable format that is defined as the Blu-Ray has been developed. The track groove in the Blu-Ray optical disc has a wobble shape, and the basic wobble pattern of the track groove is a sine/cosine wave. In the Blu-Ray optical disc, one nominal wobble length (referred to as NWL hereinafter) is equivalent to 69 channel bits, which is the minimum record unit of the Blu-Ray optical disc.
The basic pattern of the wobble is a cosine wave: cos{2π*fwob*t}, where fwob denotes the basic frequency of the wobble. Wobbles in this basic shape are called “Monotone Wobbles” (MW). In addition, some wobbles are modulated in order to carry the address information which are referred to as the ADIP (Addresses in Pre-groove), of some record units on the disc, wherein two modulation methods are involved. The first modulation method is the minimum shift keying—cosine variant (referred to as MSK-cos hereinafter), and the second method is the harmonic modulated wave (referred to as HMW hereinafter).
FIG. 1 shows the definition of the MSK mark (referred to as MM hereinafter). As shown in FIG. 1, one MSK mark consists of three NWLs with the following wobble patterns:                a first NWL starts MSK mark with a cosine wobble with a frequency 1.5*fwob,and is given by cos{2π*(1.5*fwob)*t};        a second NWL continues the MSK mark with a cosine wobble with a frequency fwob, and is given by −cos{2π*fwob*t}; and        a third NWL terminates the MSK mark with a cosine wobble with a frequency 1.5*fwob, and is given by −cos{2π*(1.5*fwob)*t}.        
FIG. 2 shows the definition of the sawtooth wobble (referred to as STW hereinafter), which is a wobble having a sawtooth-like shape. A STW is formed by combining the basic cosine wave and a sine wave of the double frequency and is given by:cos{2π*fwob*t}±a*sin{2π*(2*fwob)*t} in which a=0.25.
Such a combination of a cosine signal with the basic frequency fwob and a weighted second harmonic signal forms a sawtooth-like waveform. The “+” or “−” sign creates the left or right inclination of the waveform, where the “+” sign is used to represent a bit information of logic one, while the “−” sign is used to represent a bit information of logic zero.
FIG. 3 shows the typical ADIP structure of the Blu-Ray optical disc. The data to be recorded onto the optical disc must be aligned with the ADIP addresses which are modulated in the wobble. As shown in FIG. 3, 56 NWLs correspond to two recording frames and each group of 56 NWLs is called an ADIP unit. Each recording frame includes 1932 channel bits containing a sync filed and a data field. Moreover, two adjacent ADIP units are separated by a recording frame having a period of about 9.5 wobble cycles.
FIG. 4 shows the format of an ADIP unit. As shown in FIG. 4, the following types of ADIP units are defined:                monotone unit: consisting of 1 MM followed by 53 MW;        reference unit: consisting of 1 MM followed by 15 MW, 37 STW, and 1 MW;        sync—0 unit: consisting of 1 MM followed by 13 MW, 1 MSK mark, 7 MW, 1 MM, and 27 MW;        sync—1 unit: consisting of 1 MM followed by 15 MW, 1 MSK mark, 7 MW, 1 MM, and 25 MW;        sync—2 unit: consisting of 1 MM followed by 17 MW, 1 MM, 7 MW, 1 MM, and 23 MW;        sync—3 unit: consisting of 1 MM followed by 19 MW, 1 MM, 7 MW, 1 MM, and 21 MW;        data—1 unit: consisting of 1 MM followed by 9 MW, 1 MM, 3 MW, 37 STW, and 1 MW; and        data—0 unit: consisting of 1 MM followed by 11 MW, 1 MM, 1 MW, 37STW, and 1 MW.        
The four kind of sync units are used for synchronization purpose, the data—1 unit is used to represent a bit information of logic one, and the date—0 unit is used to represent a bit information of logic zero. Hence, the ADIP addresses on the optical disc are positioned according to the unit types of the above-mentioned ADIP unit. So, in order to judge the unit types of the ADIP unit correctly, it is an important subject to correctly detecting the information carried by the STW.